Radio handset and position location system

ABSTRACT

A radio handset includes: a signal receiver for receiving signals from a plurality of radio stations; a reception timing analyzer for analyzing reception timings of signals received by the signal reception means; a radio station selector for selecting radio stations to be used in a position calculation; and a position calculator for calculating a position of a signal reception point by using the reception timings of the signals from the selected radio stations. The radio station selector selects the radio stations to be used in the position calculation in such a manner that when reception timings of signals from two or more of the radio stations cannot be separated from one another, it is decided to exclude a signal from at least one of these radio stations.

BACKGROUND OF THE INVENTION

The present invention relates to a radio handset for detecting itscurrent position using a radio signal and in particular, to a radiohandset and a position location system for accurately identifying itscurrent position even when it is difficult to discriminate a basestation from which the signal has been transmitted.

In a mobile communication system, there has been suggested a techniqueto detect a position of a radio handset by using a signal transmittedfrom a base station. For example, JP-A-7-181242 (laid open on Jul. 21,1995) discloses a technique for detecting a handset position by usingpositions of base stations and propagation delay time differencesbetween signals transmitted to a handset from different base stations ina code division multiple access (CDMA) system.

For example, in a radio communication system shown in FIG. 11, a radiohandset 800 receives signals from three cellular phone base stations801, 802, and 803. The radio handset 800 calculates signal propagationtime differences, i.e., [propagation time of the signal transmitted fromthe base station 801—propagation time of the signal transmitted from thebase station 802] and [propagation time of the signal transmitted fromthe base station 801—propagation time of the signal transmitted from thebase station 803]. Using the propagation time differences, the radiohandset 800 calculates a current position of the radio handset 800.

Here, explanation will be given on a system based on the EIA/TIA-95specified by the TIA (Telecommunication Industry Association) which isan US CDMA digital moving communication system. In the EIA/TIA-95system, all the base stations use the same spread code (PN code).Moreover, each of the base stations has a pilot PN offset (PN offsetvalue) as a transmission time difference predetermined for each of thebase stations for identification thereof and transmits a signal at atiming shifted from the standard timing by its PN offset value.

A radio handset calculates correlation between the received signal andthe PN code so as to obtain a delay profile. For example, a correlationvalue between the received signal and the PN code is calculated by usinga matched filter, the matched filter outputs a delay profile as shown inFIG. 12.

In FIG. 12, 901. 902, and 903 shows correlation values corresponding tosignals received from the base stations 801, 802, and 803, respectively.Here, since the base stations have different PN offset values, thecorrelation values corresponding to the signals from the base stationsare temporally separated from one another. Accordingly, in the delayfile, it is possible to isolate each of the signals transmitted from thedifferent base stations as well as received timings of the signals fromthe base stations. Thus, it is possible to detect a location by usingthe signal propagation time from the base stations.

SUMMARY OF THE INVENTION

However, in a large city where base stations are concentrated, there isa case that base stations having the same PN offset value are located inthe proximity to each other. For example, when one and the same PNoffset is assigned to the base station 801 and the base station 802, adelay profile waveform as shown in FIG. 13 is obtained as matched filteroutputs corresponding to the base stations 801, 802, and 803. That is,since the base stations 801 and 802 have the same PN offset value,correlation values corresponding to the signals received from these basestations are overlapped at the same time as a delay profile waveform(matched filter output).

Thus, when the received signals appear almost at the same time in thedelay profile, it is difficult to isolate, according to the basestation, a received timing of one signal from another signal. That is,there is a high possibility that this correlation value 910 isincorrectly correlated to a signal from a particular base station. Sucha mistake introduces a large error to the propagation time measurementof signals from the respective base station, thereby deteriorating thelocation accuracy. This means that a user cannot receive an appropriatelocation information service. That is, benefit of the locationinformation service is diminished.

It is therefore an object of the present invention to provide a radiohandset capable of accurately measuring its current position even whenit is difficult to isolate respective signals from different basestations.

The radio handset according to an aspect of the present inventionincludes: signal reception means for receiving signals from a pluralityof radio stations; reception timing analysis means for analyzingreception timings of signals received by the signal reception means;radio station selection means for selecting radio stations to be used ina position calculation; and position calculation means for calculating aposition of a signal reception point by using the reception timings ofthe signals from the selected radio stations; wherein the radio stationselection means selects the radio stations to be used in the positioncalculation in such a manner that when reception timings of signals fromtwo or more of the radio stations cannot be separated from one another(for example, when a plurality of radio stations have an identical PNoffset value and a delay profile base don the signals from two or moreradio stations are overlapped), it is decided to exclude a signal fromat least one of these radio stations.

According to another aspect of the present invention, the radio handsetincludes reception means for receiving signals from a plurality of radiostations, delay profile creation means for creating a delay profile ofthe signals received by the reception means, and informationtransmission means for transmitting information used for calculating aposition of a reception point using the delay profile, wherein whensignals from two or more radio stations cannot be separated from oneanother in the delay profile (for example, when a plurality of radiostations have an identical PN offset value), the informationtransmission means transmits information used to exclude at least one ofthe signals from these radio stations.

According to still another aspect of the present invention, there isprovided a position location system including a plurality of radiostations for transmitting signals to a radio handset, reception meansfor receiving signals from the plurality of radio stations, and a radiohandset having delay profile creation means for analyzing a delayprofile of signals received by the reception means, wherein positioncalculation means is built in the radio handset or is providedseparately for calculating a position of a reception point by using thedelay profile, and wherein the position calculation means calculates theposition in such a manner that when signals from two or more of theradio stations cannot be separated from one another in the delay profile(for example, when the plurality of radio stations have the same PNoffset value), at least one signal thereof is excluded from the positioncalculation.

According to yet another aspect of the present invention, there isprovided a position calculation apparatus including radio stationselection means for selecting radio stations to be used in a positioncalculation, and position calculation means for calculating a positionof a reception point by using reception timings of signals received by aradio handset from a plurality of radio stations, wherein in casereception timings of signals from two or more of the radio stationscannot be separated from one another (for example, when a plurality ofradio stations have an identical PN offset value and delay profilesbased on the signals from these radio stations are overlapped), theradio station selection means selects radio stations to be used in aposition calculation in such a manner that a signal from at least one ofthese radio station is excluded.

In the radio handset according to the aforementioned aspects of thepresent invention, in case reception timings of signals from two or moreradio stations cannot be separated from one another, radio stationselection means excludes a signal from at least one of these radiostations when selecting radio stations to be used in the positioncalculation. Accordingly, even in an area where radio stations having anidentical PN offset value are located in the proximity from each other,it is possible to calculate a current position of the handset with ahigh accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a configuration of a radio communication system accordingto an embodiment of the present invention.

FIG. 2 is a flowchart showing a position calculation operation by theradio handset according to a first embodiment.

FIG. 3 is a flowchart showing a detailed operation for selecting a basestation in the position calculation operation according to the firstembodiment.

FIG. 4 is a flowchart showing a detailed operation for selecting a basestation in a position calculation operation according to a secondembodiment.

FIG. 5 is a flowchart showing a detailed operation for selecting a basestation in a position calculation operation according to a thirdembodiment.

FIG. 6 shows a relationship between reception timings in the thirdembodiment.

FIG. 7 is a flowchart showing a position calculation operation by aradio handset according to a fourth embodiment.

FIG. 8 shows a configuration of a mobile communication system accordingto an embodiment of the present invention.

FIG. 9 is a block diagram of a radio handset according to an embodimentof the present invention.

FIG. 10 is a block diagram of a position information server according toan embodiment of the present invention.

FIG. 11 shows a configuration of a conventional radio communicationsystem.

FIG. 12 shows a delay profile in the conventional radio communicationsystem.

FIG. 13 shows another delay profile in the conventional radiocommunication system.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Description will now be directed to embodiments of the present inventionwith reference to the attached drawings.

FIG. 1 shows a radio communication system (mobile communication system)in which a radio handset according to an embodiment of the presentinvention performs a position measurement.

Around a radio handset 100, such as a cellular telephone, cellulartelephone base stations for communication with the radio handset 100 areprovided. For base stations 101, 103, and 104, different PN offsetvalues PN1, PN3, and PN4 are assigned. The same offset value PN2 isassigned for the base stations 102 and 105.

In the embodiment of the present invention, the radio handset 100receives signals transmitted from the base stations 101 to 105. theradio handset 100 measures a propagation distance difference accordingto the propagation time differences of the signals from at least threebase stations and detects a position of the radio handset bytrilateration, assuming that positions of the three base stations areknown.

FIG. 2 is a flowchart showing a procedure for calculating the positionof the radio handset according to the first embodiment of the presentinvention.

Firstly, the radio handset 100 selects candidate base stations for theposition calculation (step 700). For example, the radio handset 100selects base stations 101 to 105 assumed to be in the vicinity from abase station list stored in advance.

Next, the radio handset 100 calculates correlation values of the signalstransmitted from the base stations 101 to 105 with the PN codes andcreates a delay profile (step 701). For example, when a correlationvalue is calculated between a received signal and a PN code using amatched filter, a delay profile waveform is obtained as an output of thematched filter. From the delay profile waveform, the timing having themaximum correlation value is extracted as a reception timing so as tomeasure reception timings of the signals transmitted from the basestations (step 702).

As for the base stations having the same PN offset, the one to be usedfor the position calculation is selected so as to prevent deteriorationof position measurement accuracy due to an incorrect identification ofthe base stations (step 703). The method of this selection procedurewill be detailed later with reference to FIG. 3.

Next, using the signals of the base stations selected for the positioncalculation in step 703, the position of the radio handset 100 iscalculated (step 704).

FIG. 3 is a flowchart showing a detailed procedure of the base stationselection in step 703.

The radio handset 100 which measured the reception timings of thesignals from the different base stations in step 702 decides whether anytwo of the base stations have an identical PN offset value (step 201).If no base stations have an identical PN offset (No in step 201), thenthe signals transmitted from the base stations are not overlapped and itis decides to use all of the candidate base stations selected in step700 (step 203).

On the other hand, if any two of the base stations have an identical PNoffset (Yes in step 201), the signals from the base stations having theidentical PN offset value are received as having an overlapped delayprofile. Since it is difficult to separate these signals, it is decidednot to use the base stations having an identical PN offset (step 202).

As has been described above, in the first embodiment of the presentinvention, none of the base stations having an identical PN offset valueare used for the position calculation. That is, in the radiocommunication system shown in FIG. 1, the base station 102 and basestation 105 are both excluded from the position calculation. Thus, evenin a region where base stations having an identical PN offset value arearranged in the proximity from each other, it is possible to preventdeterioration of the position accuracy in the radio handset due to thesignals from base stations having the identical PN offset value.

Moreover, even in such an area, it is possible to provide an accurateposition information service to a user. This increases the service areaof the position information, thereby enhancing the convenience of theposition information service.

FIG. 4 is a flowchart showing a detailed procedure of the base stationselection involved in the position calculation according to a secondembodiment of the present invention.

In the second embodiment shown in FIG. 4, the base station selectionoperation is different from that (step 703 in FIG. 2) of the firstembodiment explained with reference to FIG. 2 and FIG. 3, but maintainssome identical operations in FIG. 2.

The radio handset 100 which measured reception timings of the signalsfrom the base stations in step 702, firstly calculates a provisionalposition of the radio handset 100 (step 300). For example, theprovisional position is a position of the base station to which theradio handset 100 has transmitted a position registration signal.Moreover, the provisional position may be the result of calculationusing the candidate base stations selected in step 700 (FIG. 2)excluding the base stations having an identical PN offset value.

Among the candidate base stations selected in step 700 (FIG. 2), thosebase stations having an identical PN off set value are selected. In theradio communication system shown in FIG. 1, the base stations 102 and105 having the identical PN offset value are selected (step 301).

Next, a distances between the provisional position of the radio handsetand the base stations 102 and 105 having the identical PN offset valueare calculated, respectively (step 302). That is, the distance 122between the provisional position of the radio handset 100 and the basestation 102 and the distance 125 between the provisional position of theradio handset 100 and the base station 105 are calculated.

Next, a difference between the distances from the provisional positionof the radio handset to the base stations having the identical PN offsetvalue is compared to a predetermined value (threshold value) (step 304).According to the comparison result, it is decided whether to involve thebase stations having the identical PN offset value in the positioncalculation.

That is, a difference between the distance 122 and the distance 125 fromthe provisional position of the radio handset 100 to the base stations102 and 105 having the identical PN offset value is compared to thepredetermined threshold value (step 304). If the difference between thedistance 122 and the distance 125 exceeds the threshold value, i.e., ifthe distance to the base station 102 is not near to the distance to thebase station 105 and the signal propagation time values from these basestations are different, then it is possible to isolate each of thesignals from these base stations, and the base station nearest to theprovisional position of the radio handset 100 is selected so as to beadded to the position calculation (step 306).

More specifically, it is decides to use, in the position calculation,not only the base stations 101, 103, and 104 having different PN offsetvalues but also the base station 105 nearest to the provisional positionof the radio handset among the base stations 102 and 105 having theidentical PN offset value. The reception timings of the signalsappearing as overlapped in the delay profile are used in the positioncalculation, as that of the base station nearest to the provisionalposition.

On the other hand, when the difference between the distance 122 and thedistance 125 is less than the predetermined threshold value, i.e., whenthe distance to the base station 102 is almost identical to the distanceto the base station 105 and the propagation delay time values are almostidentical, it is difficult to separate the signals from these stationsfrom each other and the system excludes the base stations having theidentical PN offset from the position calculation (step 305). Morespecifically, neither of the base stations 102 or 105 having theidentical PN offset value is used in the position calculation, and onlythe base stations 101, 103, and 104 having different PN offset valuesare used in the position calculation.

As has been explained above, in the second embodiment of the presentinvention, one of the base stations having an identical PN offset valuewhich is estimated to be nearer to the radio handset is selected for usein the position calculation. That is, in the radio communication systemshown in FIG. 1, the signal from the base station 105 which is locatednearer than the base station 102 is used in the position calculationwhile excluding the signal from the base station 102 located farther.Accordingly, even in a region where base stations having an identical PNoffset value are located in the proximity to each other, it is possibleto calculate the position of the radio handset with a high accuracy,thereby providing an accurate position information service to userswhile enlarging the position information service area and enhancing thebenefit of the position information service.

Moreover, when the difference between the distances to the differentbase stations having an identical PN offset value is small, it isdifficult to identify the base station from which the signal has beentransmitted and accordingly all the base stations having the identicalPN offset value are excluded in the position calculation of a radiohandset. This enables to detect the position of the handset moreaccurately.

FIG. 5 is a flowchart showing a detailed procedure for selecting basestations involved in the position calculation according to a thirdembodiment of the present invention.

In the third embodiment shown in FIG. 5, the procedure for selectingbase stations is different from that (step 703 in FIG. 2) of the firstembodiment explained with reference to FIG. 2 and FIG. 3 but maintainssome identical processing steps in FIG. 2.

In step 702 the radio handset 100, which has measured reception timingsof signals from different base stations, firstly, calculates aprovisional position of the radio handset 100 (step 400). For example,this provisional position is calculated, as has been described above, asthe position of the base station to which the radio handset 100 hastransmitted the position registration signal for the radio communicationsystem, or a result of the position calculation using the candidate basestations selected in step 700 (FIG. 2) excluding those base stationshaving an identical PN offset value.

Next, the base stations having the identical PN offset value areselected from the candidate base stations selected in step 700 (FIG. 2).In the radio communication system shown in FIG. 1, the base station 102and the base station 105 having the identical PN offset value areselected (step 401).

Then, estimated values of timings when the signals from the basestations selected in step 401 were received by the radio handset (step402). The estimated values of the reception timings are calculated usingthe distances between the provisional position of the radio handset 100and the base stations 102 and 103 calculated in step 400. That is, eachof the distances from the base stations is divided by the propagationvelocity (light velocity) to obtain a propagation time so as tocalculate the estimated value of the reception timing.

Next, the measured value obtained in step 702 (FIG. 2), i.e., thereception timing of the signals received from the base stations havingthe identical PN offset value and appearing as overlapped delay profilemeasured in step 702 (FIG. 2), is compared to the value obtained in step402, i.e., the estimated value of the reception timing for the basestations having the identical PN offset value, and a difference betweenthese values is calculated as a reception timing error (step 403).

The error, i.e., the difference between the reception timing estimatedvalue and the reception timing measured value calculated for each of thebase stations having the identical PN offset value is further processedby calculating a difference between these differences (errors)calculated for the different base stations having the identical PNoffset value (step 404). That is, a difference between the receptiontiming error calculated for the bas station 102 and the reception timingerror calculated for the base station 105 is calculated.

Next, the difference between the error calculated for each of the basestations having the identical PN offset value is compared to apredetermined threshold value (step 405). According to this comparisonresult, it is decided whether to use the base stations having theidentical PN offset and subjected to the comparison, in the positioncalculation.

That is, the difference between the reception timing error for the basestation 102 and the reception timing error for the base station 105 withthe identical offset value is compared to the predetermined thresholdvalue (step 405). If the difference between the reception timing errorfor the base station 102 and the reception timing error for the basestation 105 exceeds the predetermined threshold value, i.e., when adifference between the distance to the base station 102 and the distanceto the base station 105 is not small and the signal propagation timefrom the base station 102 is different from the signal propagation timefrom the base station 105, it is possible to isolate the signal of thebase station 102 from the signal of the base station 105. In this case,the base station having the smallest reception timing error is selectedfrom the base stations having the identical PN offset value and it isdecided to use the this base station having the smallest receptiontiming error in the position calculation (step 406). Here, the basestation giving the smallest reception timing error is selected in theposition calculation because the signal received in an overlapped mannerhas the highest possibility that the signal is from the base stationwhich has transmitted the signal received at the earliest point with thesmallest reception timing error.

More specifically, it is decided to perform the position calculationusing the base stations 105 having the minimum error between thereception timing estimated value and the reception timing measuredvalue, in addition to the base stations 101, 103, and 104 havingdifferent PN offset values. The reception timing of the signalsappearing as overlapped in the delay profile is used as the base stationhaving the minimum reception timing error.

On the other hand, when a difference between the reception timing errorfor the base station 102 and the reception timing error for the basestation 105 is smaller than the predetermined threshold value, it isdifficult to separate the signals from these stations from each otherand the system excludes from the position calculation the base stationshaving the identical PN offset value (step 407). More specifically, thesystem does not use in the position calculation either of the basestations 102 and 105 with the identical PN offset value and only thebase stations having different PN offset values.

FIG. 6 shows a relationship between signal reception timings when thethird embodiment (FIG. 5) is applied to the radio communication systemshown in FIG. 1. FIG. 6 shows the reception timing measured valuescalculated in step 702 and the reception timing estimated valuescalculated in step 402 (FIG. 5).

In the radio communication system shown in FIG. 1, an identical PNoffset value is assigned to the base station 102 and the base station105. Since a signal from the base station 102 and a signal from the basestation 105 have the identical offset value, a delay profile analysis isperformed using a matched filter and a reception timing measured value410 is obtained at a temporally overlapped timing (step 702).

Moreover, using the provisional position of the radio handset 100 andthe position of the base station 102, a distance between them isobtained. This distance is divided by light velocity to obtain apropagation delay time, which is used to obtain an estimated value ofreception timing of the signal from the base station 102. In the sameway, a reception timing estimated value is obtained for the base station105 having the PN offset value identical to that of the base station 102(step 402). These reception timing estimated values are indicated by 411and 412, respectively in FIG. 6.

Differences between the reception timing measured values obtained instep 702 and the corresponding reception timing estimated valuesobtained in step 402 are calculated as reception timing errors (step403). The reception timing errors are indicted by 414 and 413 in FIG. 6.

Next, a difference between the reception timing errors, i.e., the error413 and the error 414, is calculated for the base stations 102 and 105having the identical PN offset value (step 404).

Next, the difference (error 414—error 413) calculated in step 404 iscompared to a predetermined threshold value to decide whether to use inthe position calculation, the base station having the smallest receptiontiming error among the base stations having the identical PN offsetvalue.

As has been described above, in the third embodiment of the presentinvention, among the base stations having an identical PN offset, a basestation having the smallest reception timing error, i.e., for which theestimated value is near to the actual reception timing is selected to beused in the position calculation. That is, in the radio communicationsystem shown in FIG. 1, the signal from the base station 105 having thesmallest reception timing error is used in the position calculation,excluding the signal from the base station 102 having a large receptiontiming error. Accordingly, even when base stations having an identicalPN offset value are located in the proximity to each other, it ispossible to calculate the position of the radio handset with a highaccuracy, thereby enabling to provide an accurate position informationservice. This enlarges the position information service area, enhancingthe benefit of the position information service.

Moreover, if a difference between the reception timing errors of thesignals from the base stations with an identical PN offset value issmall, it is difficult to identify the base station from which a signalhas been transmitted, and the base stations having the identical PNoffset value are excluded when calculating the position of the radiohandset. This provides a more accurate position of the radio handset.

FIG. 7 is a flowchart indication a procedure for calculating a positionof the radio handset according to a fourth embodiment of the presentinvention.

In the fourth embodiment shown in FIG. 7, the method for selecting basestations to be used in the position calculation (steps 710 to 714) isdifferent from that of the first embodiment explained with reference toFIG. 2 and FIG. 3 but maintains the same processes in steps 700 to 702shown in FIG. 2.

Firstly, the radio handset 100 selects candidate base stations to beused in the position calculation (step 700). For example, base stations101 to 105 estimated in the vicinity are selected from a base stationlist stored in the radio handset 100.

Next, the radio handset 100 calculates correlation values between thesignals received from the base stations 101 to 105 with the PN codes soas to create a delay profile (step 701). For example, a matched filteris used to calculate a correlation value between a received signal and acorresponding PN code. Thus, as an output from the matched filter, adelay profile waveform is obtained. According to this delay profile, theearliest timing having the maximum correlation value is extracted as areception timing, thereby measuring reception timings of signals fromthe base stations (step 702).

With some of the candidate base stations selected in step 700 to be usedin the position calculation, a combination of base stations Cj (j=1, . .. , M) is decided (step 710). This base station combination is decidedso as to contain one base station having an identical PN offset value,i.e., only one of the base stations with the identical PN offset valueis contained in the combination. More specifically, in the radiocommunication system shown in FIG. 1, a first combination of basestations consists of the base stations 101, 102, 103, and 104 and asecond combination of base stations consists of the base stations 101,103, 104, and 105. Thus, in step 710, the base station combination isdetermined in such a manner that only one of the base stations havingthe identical PN offset value is contained in one combination, i.e., thebase stations 102 and 105 having the identical PN offset value cannot becontained in one combination.

By using the base stations combination Cj (j=1, . . . , M) decided instep 710, positions of the respective reception points are calculated toobtain a position calculation result (Xj, Yj) for each of the basestation combinations (step 711).

For the position calculation result (Xj, Yj) calculated in step 711, aposition measurement error is calculated using an error function valueF(j). This position measurement error can be calculated, for example, byusing an equation as follows. $\begin{matrix}{{F(j)} = {\frac{1}{N}{\sum\limits_{j = 1}^{N}\quad \left\lbrack {\left\{ \sqrt{\left( {X_{j} - {BX}_{0}} \right)^{2} + \left( {Y_{j} - {BY}_{0}} \right)^{2}} \right. - \left. {\left. \sqrt{\left( {X_{j} - {BX}_{1}} \right)^{2} + \left( {Y_{j} - {BY}_{1}} \right)^{2}} \right\} - {C\left( {T_{0} - T_{1}} \right)}} \right\rbrack^{2}} \right.}}} & (1)\end{matrix}$

wherein

C . . . light velocity

(Xj, Yj) . . . result of the radio handset position calculation usingthe base station combination Cj

(BXi, BYi) . . . position of a base station i

Ti . . . result of reception timing measurement of the signal from thebase station i

Here, in the Equation 1, the first term in the right side within { } isa distance between the radio handset and a base station 0 calculatedfrom coordinates on a map, and the second term in the right side within{ } represents a distance between the radio handset and the base stationi. Accordingly, the value obtained in { } represents a differencebetween the distance from the base station 0 (serving as a reference)and a distance from the i-th base station. Moreover, the third term inthe right side represents a difference between: a distance between theradio handset and the reference base station 0 obtained from thereception timing measurement result, and a distance between the radiohandset and the base station i. When the reception timings are correctlymeasured, the difference between these two distances approaches to 0.Accordingly, it is possible to decide that as the value of F(i) becomessmaller, more accurate position of the radio handset is obtained.

Then, a jMIN minimizing the value of the error function value F(j)corresponding to the base station combination Cj calculated in step 712is selected (step 713), and a position calculation result (XjMIN,Y&jMIN) corresponding to the jMIN is selected. This position calculationresult is determined to the position of the radio handset. As is clearfrom the aforementioned, “N” in the aforementioned Equation, is thenumber of base stations belonging to Cj deleted by 1.

A specific example will be explained by applying this fourth embodimentto the radio communication system shown in FIG. 1. By using thecombination of the base stations 101, 102, 103, and 104 and thecombination of the base stations 101, 103, 104, and 105, the radiohandset position is calculated (step 711) and by using the errorfunction value F(j), the position measurement error is calculated (step712). Then the radio handset position calculated by using the basestation combination having a smaller error function value is decided tobe a position calculation result (steps 713 and 714).

As has been described above, in the fourth embodiment of the presentinvention, a plurality of combinations each containing only one of thebase stations having an identical PN offset value are created and theposition accuracy of the radio handset is calculated by selecting a basestation combination having the smallest position error. That is, the oneof the base stations having an identical PN offset value giving aminimum position error is selected for calculating the position of theradio handset. Accordingly, even if the base stations having anidentical PN offset value are located in the proximity from each other,it is possible to calculate the position of the radio handset with ahigh accuracy.

FIG. 8 shows a configuration related to the position calculation in themobile communication system in which the radio handset according to theembodiment of the present invention performs position calculation.

The radio handset 2 selects an base station 1 appropriate forcommunication, from a plurality of base stations, and communicates withthe base station 1 via a radio line 5. Moreover, for hand-over or thelike, the radio handset 2 receives a signal from a base station otherthan the base station 1 where the radio line 5 is currently set. Byusing signals received from the plurality of base stations, the positionof the radio handset 2 is measured.

The base station 1 is connected to a public network 3 and serves ascommunication means between the radio handset 2 and anothercommunication device (not depicted) connected to the public network 3.Moreover, the base station 1 communicates with a position informationserver 4 connected to the public network 3 and transmits/receivesinformation required for the position calculation.

FIG. 9 is a block diagram showing a configuration of the radio handset2.

A signal from the base station 1 is received by an antenna 10 andtransmitted to a signal receiver 11. The signal receiver 11 includes aradio block (receiver/transmitter) and a base-band processing block. Theradio block performs amplification of a higher frequency signal and anintermediate frequency signal and a reception of frequency conversion.The base-band processing block performs demodulation of a base-bandsignal.

The signal processed in the signal receiver 11 is fed to a delay profilecalculator 12. The delay profile calculator 12, for example, includes amatched filter and calculates a correlation value between a receivedsignal and a corresponding PN code for each reception timing so as tocreate a delay profile indicating a value corresponding to a correlationvalue in each of the reception timings.

The delay profile created in the delay profile calculator 12 is storedand retained in a delay profile memory 13. According to software storedin a storage device 15 (such as a memory), a CPU 14 executes processingrequired for the position calculation by using the delay profile storedin the delay profile memory 13.

The radio handset 2 may be configured in such a manner that the delayprofile calculator 12 and the delay profile memory 13 are arranged as asingle semiconductor device (LSI) which is connected to the CPU 14.Moreover, it is possible to constitute a single LSI by the delay profilecalculator 12, the delay profile memory 13, and the CPU 14, which isconnected to the storage device 15. Furthermore, it is also possible toconstitute a single LSI by the delay profile calculator 12, the delayprofile memory 13, the CPU 14 and the storage device 15.

FIG. 10 shows a configuration example of the position information server4. A CPU 20 executes data communication to/from the public network 3according to software stored in a storage device. More specifically,information related to the base stations (including positions and PNoffset values of the base stations) is stored in the positioninformation server 4 and transmitted to the radio handset 2 according toa request from the radio handset 2. Moreover, by using a delay profilebased on signals received by the radio handset 2 from base stations, theposition of the radio handset 2 is calculated.

Next, explanation will be given regarding how the position calculationshown in FIG. 2 is performed by the radio handset 2.

Firstly, the CPU 14 of the radio handset 2 selects candidate basestations to be used in the position calculation (step 700). The signalreceiver 11 receives signals from the candidate base stations, and thedelay profile calculator 12 calculates a correlation value between thereceived signal and the corresponding PN codes to create a delay profile(step 701), which is stored in the delay profile memory 13.

Next, the CPU 14 extracts signal reception timings from the candidatebase stations in the delay profile stored in the delay profile memory 13and measures reception timings of the signals from the base stations(step 702). Then, the CPU 14 decides whether to use in the positioncalculation those signals transmitted from base stations having anidentical PN offset value and selects base stations to be used in theposition calculation (step 703), thereby calculating the position of theradio handset 2 (step 704).

The position of the radio handset 2 thus calculated may be used by theCPU 14 (radio handset 2) or reported via the base station 1 and thepublic network 3 to the position information server 4 where the positioninformation can be used.

Next, explanation will be given when the position calculation processingshown in FIG. 2 is divided into two parts performed by the radioterminal 2 and the position information server 4.

Firstly, the CPU 14 of the radio handset 2 selects candidate basestations for use in the position calculation (step 700). The signalreceiver 11 receives signals from the candidate base stations. The delayprofile calculator 12 calculates correlation values between the receivedsignals and the corresponding PN codes to create a delay profile (step701), which is stored in the delay profile memory 13.

After this, the CPU 14 extracts reception timings of the signals fromthe candidate base stations in the delay profile stored in the delayprofile memory 13 and measure the reception timings of the signals fromthe base stations (step 702). Then, the CPU 14 reports the receptiontimings of the signals from the base stations obtained in step 702, viathe base station 1 and the public network 3 to the position informationserver 4.

By using the reception timings of the signals from the aforementionedbase stations, the CPU 20 in the position information server 4 decideswhether to use in the position calculation, the signals from the basestations having an identical PN offset and selects base stations to beused in the position calculation (step 703), after which the CPU 20calculates the position of the radio handset 2 (step 704). The positionof the radio handset 2 obtained in this step 704 may be utilized in theCPU 20 (position information server 4) or may be reported via the publicnetwork 3 and the base station 1 to the radio handset 2.

Thus, instead of performing all the steps of the position calculation inthe radio handset 2, the position calculation processing is partiallyperformed in the position information server 4 connected to the basestation 1. That is, a complicated process can be executed in theposition information server 4 having a large computation capacity, andthe position of the radio handset 2 can be calculated with a high speedwithout applying a large processing load to the radio handset 2.

Next, explanation will be given on the processing of the positioncalculation shown in FIG. 7 is performed.

Firstly, the CPU 14 of the radio set 2 selects candidate base stationsto be used in the position calculation (step 700). The signal receiver11 receives signals from the candidate base stations. The delay profilecalculator 12 calculates correlation values between the received signalsand corresponding PN codes to create a delay profile (step 701) andstores the profile in the delay profile memory 13.

After this, the CPU 14 extracts reception timings of the candidate basestation in the delay profile stored in the delay profile memory 13 andmeasures reception timings of signals from the base stations (step 702).Then, the CPU 14 decides combinations of base stations to calculate aposition of the radio handset 2 (steps 710 to 714). The position of theradio handset 2 obtained in step 714 may be used in the CPU 14 (radiohandset 2) or may be reported via the base station 1 and the publicnetwork 3 to the position information server 4 so that the positioninformation is utilized later.

Next, explanation will be given on the position calculation processingshown in FIG. 7 divided into two parts to be performed in the radiohandset 2 and the position information server 4.

Firstly, the CPU 14 of the radio handset 2 selects candidate basestations to be used in the position calculation (step 700). The signalreceiver 11 receives signals from the candidate base stations. The delayprofile calculator 12 calculates correlation values between the receivedsignals and corresponding PN codes to create a delay profile (step 701)and stores the profile in the delay profile memory 13.

After this, the CPU 14 extracts reception timings of the signals fromthe candidate base stations, from the delay profile stored in the delayprofile memory 13 and measures reception timings of the signals from thebase stations (step 702). Then, the CPU 14 reports the reception timingsof the signals from the base stations obtained in step 702, via the basestation 1 and the public network 3 to the position information server 4.

The CPU 20 of the position information server 4 uses the receptiontimings of the signals from the respective base stations for executingthe processes for deciding combinations of the base stations up to aprocess for calculating the position of the radio handset 2 (steps 710to 714). The position of the radio handset 2 obtained in step 714 may beused in the CPU 14 (radio handset 2) or may be reported to via the basestation 1 and the public network 3 to the position information server 4so that the position information is utilized later.

Thus, instead performing all the steps of the position calculation inthe radio handset 2, the position calculation is partially performed inthe position information server 4 connected to the base station 1. Thatis, a complicated process can be performed in the position informationserver 4 having a large computation capacity. This enables to calculatethe position of the radio handset 2 with a high speed without applying alarge processing load to the radio handset 2.

The followings are representative aspects of the present invention inaddition to those described in Claims.

A position location system comprising: a plurality of radio stations fortransmitting signals to a radio handset; reception means for receivingsignals from the plurality of radio stations; a radio handset havingdelay profile creation means for analyzing a delay profile of thesignals received by the reception means; and position calculation meansbuilt in the radio handset or provided separately for calculating aposition of a reception point by using the delay profile;

wherein the position calculation means calculates the position in such amanner that when signals from two or more of the radio stations cannotbe separated from one another in the delay profile (for example, whenthese radio stations have an identical PN offset value and signalstherefrom cannot be identified in the delay profile), at least onesignal thereof is excluded from the position calculation, and

the position calculation means performs position calculation withoutusing signals whose reception timings cannot be separated from oneanother except for the radio station located at the shortest distancefrom a provisional position.

A position location system comprising: a plurality of radio stations fortransmitting signals to a radio handset; reception means for receivingsignals from the plurality of radio stations; a radio handset havingdelay profile creation means for analyzing a delay profile of thesignals received by the reception means; and position calculation meansbuilt in the radio handset or provided separately for calculating aposition of a reception point by using the delay profile;

wherein the position calculation means calculates the position in such amanner that when signals from two or more of the radio stations cannotbe separated from one another in the delay profile (for example, whenthese radio stations have an identical PN offset value and signalstherefrom cannot be identified in the delay profile), at least onesignal thereof is excluded from the position calculation, and

further reception timing error estimation means is provided forestimating reception timing errors of the signals from the radiostations, and

the position calculation means performs a position calculation withoutusing signals whose reception timings cannot be separated from oneanother except for the radio station having the smallest signalreception error (the error in this case is, for example, a differencebetween a propagation time of the signal from the radio station and apropagation time obtained from the position of the radio station and aprovisional position of a reception point).

A position calculation apparatus including radio station selection meansfor selecting radio stations to be used in a position calculation, andposition calculation means for calculating a position of a receptionpoint by using reception timings of signals received by a radio handsetfrom a plurality of radio stations, wherein in case reception timings ofsignals from two or more of the radio stations cannot be separated fromone another (for example, when a plurality of ratio stations have anidentical PN offset value and delay profiles based on the signals fromthese radio stations are overlapped, disabling to separate receptiontimings of signals from these radio stations), the radio stationselection means selects radio stations to be used in a positioncalculation in such a manner that a signal from at least one of theseradio station is excluded, and

the radio station selection means selects radio stations to be used in aposition calculation in such a manner that the signals whose receptiontimings cannot be separated from one another are not used in theposition calculation except for the radio station located at theshortest distance from the provisional position.

A position calculation apparatus including radio station selection meansfor selecting radio stations to be used in a position calculation, andposition calculation means for calculating a position of a receptionpoint by using reception timings of signals received by a radio handsetfrom a plurality of radio stations, wherein in case reception timings ofsignals from two or more of the radio stations cannot be separated fromone another (for example, when a plurality of ratio stations have anidentical PN offset value and delay profiles based on the signals fromthese radio stations are overlapped, disabling to separate receptiontimings of signals from these radio stations), the radio stationselection means selects radio stations to be used in a positioncalculation in such a manner that a signal from at least one of theseradio station is excluded, and

the radio station selection means selects radio stations to be used in aposition calculation in such a manner signals whose reception timingscannot be separated from one another are not used in a positioncalculation except for the radio station having the smallest signalreception error (the error in this case is, for example, a differencebetween a propagation time of the signal from the radio station and apropagation time obtained from the position of the radio station and aprovisional position of a reception point).

A program causing a radio handset to execute a position calculationmethod which receives signals from a plurality of radio stations andcalculates a position of a reception point by using reception timings ofthe signals,

the program causing the radio handset to functions as

analysis means for analyzing reception timings of the signals received;

as selection means for selecting radio stations to be used forcalculation of the position; and

calculation means for calculating the position of the reception point byusing the signals from the radio stations selected;

wherein in case reception timings of signals from two or more of theradio stations cannot be separated from one another (for example, whenthe radio stations have an identical PN offset value and delay profilesbased on the signals from the two or more stations are overlapped,disabling to separate reception timings of the signals from these radiostations from one another), the radio stations to be used in calculationof the position are selected in such a manner that at least one of thesignals from these radio stations is not used in the calculation.

A semiconductor device for use in a radio handset having a receiver forreceiving signals from a plurality of radio stations and calculating aposition of a reception point by using the signals received, thesemiconductor device including:

reception timing analysis means for analyzing reception timings of thesignals received by the receiver;

radio station selection means for selecting radio stations to be used incalculating the position; and

position calculation means for calculating the position of the receptionpoint by using reception timings f the signals from the radio stationselected,

wherein in case reception timings of signals from two or more of theradio stations cannot be separated from one another (for example, whenthe radio stations have an identical PN offset value and delay profilesbased on the signals from these stations are overlapped, the receptiontimings of the signals from these stations cannot be separated from oneanother), the radio stations to be used in calculating the position areselected in such a manner that at least one of the signals from thesestations is not used.

A radio handset comprising:

reception means for receiving signals from a plurality of radiostations;

delay profile creation means for creating a delay profile of signalsreceived by the reception means; and

information transmission means for using the delay profile to receiveinformation required for calculating a position of a reception point;

wherein in case delay profiles based on signals from two or more of theradio stations cannot be separated from one another, the informationtransmission means transmits information used for excluding at least oneof the signals from the radio stations.

A radio handset comprising:

reception means for receiving signals from a plurality of radiostations;

delay profile creation means for creating a delay profile of signalsreceived by the reception means; and

information transmission means for using the delay profile to receiveinformation required for calculating a position of a reception point;

wherein in case more than one of the radio stations have an identical PNoffset value and signals from these stations cannot be separated fromone another in the delay profile, the information transmission meanstransmits information used for excluding at least one of the signalsfrom these radio stations in a position calculation.

A radio handset comprising:

reception means for receiving signals from a plurality of radiostations;

delay profile creation means for creating a delay profile of signalsreceived by the reception means; and

information transmission means for using the delay profile to receiveinformation required for calculating a position of a reception point;

wherein in case delay profiles based on signals from two or more of theradio stations cannot be separated from one another, the informationtransmission means transmits information used for excluding at least oneof the signals from these radio stations, and

the information transmission transmits information used for selectingradio stations to be used in a calculation in such a manner that none ofthe signals which cannot be separated from one another in the delayprofile are used.

A radio handset for receiving signals from a plurality of radio stationsand causing to calculate a position of a reception point, the handsetcomprising:

a receiver for receiving signals from the radio stations;

a delay profile calculator for creating a delay profile of signalsreceived by the receiver; and

a control unit for creating information used to select radio stations tobe used in a position calculation in such a manner that in case signalsfrom two or more of the radio stations cannot be separated from oneanother in the delay profile, at least one of the signals from theseradio stations is excluded from the position calculation.

A position calculation apparatus comprising:

radio station selection means for selecting radio stations to be used ina position calculation; and

position calculation means for calculating a position of a receptionpoint by using reception timings of signals from the radio stationsselected by the radio station selection means from the signals receivedby a radio handset,

wherein in case reception timings of signals from two or more radiostations cannot be separated from one another, the radio stationselection means selects radio stations to be used in a positioncalculation in such a manner that at least one of the signals from theseradio stations is not used.

A position calculation apparatus comprising:

radio station selection means for selecting radio stations to be used ina position calculation; and

position calculation means for calculating a position of a receptionpoint by using reception timings of signals from the radio stationsselected by the radio station selection means from the signals receivedby a radio handset,

wherein in case two ore more of the radio stations have an identical PNoffset value and delay profiles based on the signals from these radiostations are overlapped, disabling to separate reception timings of thesignals from these radio stations, the radio stations selection meansselects radio stations to be used in a position calculation in such amanner that at least one of the signals from these radio stations is notused in the position calculation.

A position calculation apparatus comprising:

radio station selection means for selecting radio stations to be used ina position calculation; and

position calculation means for calculating a position of a receptionpoint by using reception timings of signals from the radio stationsselected by the radio station selection means from the signals receivedby a radio handset,

wherein in case reception timings of signals from two or more radiostations cannot be separated from one another, the radio stationselection means selects radio stations to be used in a positioncalculation in such a manner that at least one of the signals from theseradio stations is not used, and

the radio station selection means selects the radio stations to be usedin the position calculation in such manner that none of the signals fromradio stations whose reception timings cannot be separated from oneanother are used in the position calculation.

A position calculation apparatus comprising position calculation means,wherein the position calculation means

calculates a position of a reception point by using reception timings ofsignals received from a plurality of radio stations including radiostations having an identical PN offset value;

calculates a position of a reception point by using signals from radiostations belonging to a first radio station group consisting of aplurality of radio stations having different PN offset values; uses thecalculation result to obtain information concerning distances from thereception point to the radio stations belonging to the first radiostation group and information concerning distances from the receptionpoint to the radio stations belonging to the first radio station groupcalculated by using a reception timing analysis result, therebyobtaining an error of the position of the reception point; and

the position calculation means further calculates the position of thereception point by using signals from radio stations belonging to asecond radio station group consisting of a plurality of radio stationshaving different PN offset values; uses the calculation result to obtaininformation concerning distances from the reception point to the radiostations belonging to the second radio station group and informationconcerning distances from the reception point to the radio stationsbelonging to the second radio station group calculated by using areception timing analysis result, thereby obtaining another error of theposition of the reception point; and

wherein the calculation result of the position of reception pointobtained by using the radio station group having a smaller error isdecided to be the position of the reception point.

What is claimed is:
 1. A radio handset comprising: signal receptionmeans for receiving signals from a plurality of radio stations;reception timing analysis means for analyzing reception timings ofsignals received by the signal reception means; radio station selectionmeans for selecting radio stations to be used in a position calculation;and position calculation means for calculating a position of a signalreception point of the handset by using the reception timings of thesignals from the selected radio stations; wherein the radio stationselection means selects the radio stations to be used in the positioncalculation in such a manner that when reception timings of signals fromtwo or more of the radio stations cannot be separated from one another,the radio station selection means excludes a signal from at least one ofsaid two or more radio stations.
 2. A radio handset as claimed in claim1, wherein the radio station selection means selects radio stations tobe used in the position calculation in such a manner that when two ormore of the radio stations have an identical PN offset value and delayprofiles based on the signals from these radio stations are overlapped,disabling to separate reception timings of the signals from thesestations from one another, a signal from at least one of said two ormore radio stations is excluded from the position calculation.
 3. Aradio handset as claimed in claim 1, wherein the radio station selectionmeans selects radio stations to be used in the position calculation,excluding all the signals from said two or more radio stations whosereception timings cannot be separated from one another.
 4. A radiohandset as claimed in claim 1, wherein a provisional positioncalculation means is provided for calculating a provisional position ofthe signal reception point, and the radio station selection meansselects the radio stations to be used in a position calculation in sucha manner that all the signals from the radio stations whose receptiontimings cannot be separated from one another are excluded except for oneof said two or more radio stations located at the shortest distance fromthe provisional position.
 5. A radio handset as claimed in claim 1,wherein a reception timing error estimation means is provided forestimating errors of the reception timings of the signals from the radiostations, and the radio station selection means selects the radiostations to be used in the position calculation in such a manner thatall the signals from the radio stations whose reception timings cannotbe separated from one another are excluded except for one of said two ormore radio stations whose signal was received at a minimum timing error.6. A radio handset as claimed in claim 5, wherein a provisional positioncalculation means is provided for calculating a provisional position ofthe signal reception point, and the reception timing error estimationmeans calculates as the reception timing error a difference between apropagation time of the signal from the radio station and a propagationtime obtained from the position of the provisional position of thesignal reception point.
 7. A radio handset comprising: reception meansfor receiving signals from a plurality of radio stations including radiostations having an identical PN offset value; reception timing analysismeans for analyzing reception timings of the signals received by thereception means; and position calculation means for calculating aposition of a reception point of the handset by using the receptiontimings of the signals from the plurality of radio stations; wherein theposition calculation means calculates the position of the receptionpoint by using signals from a first radio station group consisting of aplurality of radio stations having different PN offset values to obtaininformation concerning distances from the reception point to the radiostations of the first radio station group to be considered with thereception timing analysis result, thereby obtaining an error of theposition of the reception point; and the position calculation meansfurther calculates the position of the reception point by using signalsfrom at least one additional radio station group consisting of aplurality of radio stations having different PN offset values to obtaininformation concerning distances from the reception point to the radiostations of the additional radio station group to be considered with thereception timing analysis result, thereby obtaining another error of theposition of the reception point; and wherein the calculation result ofthe position of reception point obtained by using the radio stationgroup having a smallest error is decided to be the position of thereception point.
 8. A radio handset for calculation a position of areception point of the handset by using signals from a plurality ofradio stations, the radio handset comprising: a receiver for receivingsignals from the radio stations; a signal reception timing analyzingcircuit for analyzing reception timings of the signals received by thereceiver; and a controller for selecting radio stations to be used in aposition calculation in such a manner that when reception timings ofsignals from two or more radio stations cannot be separated from oneanother, at least one signal thereof is excluded form the positioncalculation of the reception point by using reception timings of signalsfrom the selected radio stations.
 9. A position location systemcomprising: a plurality of radio stations for transmitting signals to aradio handset; reception means for receiving signals from the pluralityof radio stations; a radio handset having delay profile creation meansfor analyzing a delay profile of the signals received by the receptionmeans; and position calculation means built in the radio handset orprovided separately for calculating a position of a reception point ofthe handset by using the delay profile; wherein the position calculationmeans calculates the position in such a manner that when signals fromtwo or more of the radio stations cannot be separated from one anotherin the delay profile, at least one signal thereof is excluded from theposition calculation.
 10. A position location system as claimed in claim9, wherein the position calculation means performs the positioncalculation in such a manner that when two or more of the radio stationshave an identical PN offset value and signals therefrom cannot beseparated from one another in the delay profile, at least one signalthereof is excluded from the position calculation.
 11. A positionlocation system as claimed in claim 9, wherein the position calculationmeans performs the position calculation including excluding all thesignals from the radio stations which cannot be separated from oneanother in the delay profile.
 12. A position location system comprising:reception means for receiving signals from a plurality of radio stationsincluding radio stations having an identical PN offset value; receptiontiming analysis means for analyzing reception timings of signalsreceived by the reception means; and position calculation means forcalculating a position of a reception point of a handset by using thereception timings of the signals from the plurality of radio stations;wherein the position calculation means calculates the position of thereception point of the handset by using signals from a first radiostation group consisting of a plurality of radio stations havingdifferent PN offset values to obtain information concerning distancesfrom the reception point to the radio stations of the first radiostation group to be considered with the reception timing analysisresult, thereby obtaining an error of the position of the receptionpoint; and the position calculation means further calculates theposition of the reception point of the hand set by using signals from atleast one additional radio station group consisting of a plurality ofradio stations having different PN offset values to obtain informationconcerning distances from the reception point to the radio stations ofthe additional radio station group to be considered with the receptiontiming analysis result, thereby obtaining another error of the positionof the reception point; and wherein the calculation result of theposition of reception point obtained by using the radio station grouphaving a smallest error is decided to be the position of the receptionpoint.